1. Field of the Invention
The present disclosure relates in general to valves for mineral recovery wells, and in particular to actuators to actuate valves.
2. Description of Related Art
A gate valve is a valve having a body and a bore through the body. A gate is positioned transverse to the body, and moves linearly to obstruct flow through the bore or allow flow through the bore. Some gates have an aperture that aligns with the bore to allow flow. The gate can be normally open, and thus the gate is closed when it is moved linearly to push the aperture out of alignment with the bore. Alternatively, a gate can be normally closed, and thus the gate is opened when it is moved linearly to position the aperture in alignment with the bore. Regardless of whether the gate is normally open or normally closed, the gate is moved, or actuated, by a valve actuator.
Actuators can be a hydraulic, piston type actuator, or actuators can be a pneumatic piston or diaphragm type actuator. In conventional diaphragm actuators, a diaphragm is moved in response to pressure media, such as gas or other fluids, urging the diaphragm toward the gate valve. The diaphragm is supported by a support plate. When the diaphragm is urged downward with the pressure media, it urges the support plate downward, which then transfers the downward force via a stem to the gate of the gate valve to open or close the gate valve, as applicable. In current diaphragm actuators a top shaft extends through an opening in the top or cap of the actuator and provides a visual position indication to show if the gate valve is open or closed or in an intermediate position between open and closed. However, actuator failure can be caused by a damaged top shaft. This can happen, for example from improper handling, during shipping, tools being dropped on the top shaft, or from service operations. A damaged top shaft can in turn damage the seals that seal the top shaft to the inner surface of the opening in the cap of the actuator, affecting whether the seals can contain the pressure of the pressure media as designed. This is particularly true if corrosive fluids are used or if the valve is located in a harsh environment.